The objective of this contract is to test approximately 25 chemicals per year for mutagenicity using the in vitro Salmonella mutagenicity test. The Salmonella test has become widely accepted as an indicator of a chemical's potential mutagenicity in higher organisms, and of carcinogenicity. The chemicals tested will be selected fromamong those that are proposed for mutagenicity, carcinogenicity, or reproductive toxicity testing, or are of special interest to the National Toxicology Program or others in the NIEHS. The results obtained from this contract will be used to assist in setting priorities for short- and longterm animal testing, and will provide information on mechanisms of action to support the interpretations of long-term animal toxicity results. Completion of these studies will also allow for the further development of the genetic toxicity data base which will be used to determine the level of agreement between in vivo and in vitro genetic toxicity tests and the predictivity of in vitro results for rodent carcinogenesis.